For voice application, there are certain hours during a business day when the voice traffic load is much heavier than the average. In order to handle the peak voice traffic load without additional radio spectrum, some network operators would like to introduce coder/decoder (CODEC) adaptation based on the load condition at the radio access network (RAN) so that, when experiencing congestion during the peak hours, an enhanced Node B (eNB), which is also known as the base station, base terminal station, controller, and so forth, can indicate to a User Equipment (UE), which is also known as mobile station, terminal, subscriber, and so on, to select a more radio resource friendly CODEC rate for voice over Internet Protocol (VoIP) applications. Thus, more voice calls may be admitted during the peak hours with the trade-off of slight degradation in voice quality.
In its technical specification Request for Comments (RFC) 3168, titled “The Addition of Explicit Congestion Notification (ECN) to IP”, the Internet Engineering Task Force (IETF) has specified two bits in the Internet Protocol (IP) header of an IP packet for providing explicit congestion notification (ECN). These two ECN bits can be used to indicate four codepoints as shown in the Table 1 below.
TABLE 1ValueName00Not-ECT (not ECN Capable Transport)01ECT(0) (ECN Capable Transport (0))10ECT(1) (ECN Capable Transport (1))11CE (Congestion Experienced)
The ECN-Capable Transport (ECT) codepoints ‘01’ and ‘10’, which are also known as ECT(0) and ECT(1) respectively, are set by the data sender to indicate that the end-points of the transport protocol are ECN-capable. The phrase “the ECT codepoint” in this invention refers to either of the two ECT codepoints. Any intermediate network node, such as a router, treats the ECT(0) and ECT(1) codepoints as equivalent. Senders are free to use either the ECT(0) or the ECT(1) codepoint to indicate ECT, on a packet-by-packet basis. The Not-ECT codepoint ‘00’ indicates a packet that is not using ECN. The CE codepoint ‘11’ is set by an intermediate node to indicate congestion to the endpoints.
In RFC 3168, the IETF has further specified two bits in the Transmission Control Protocol (TCP) header, namely ECN-Echo (ECE) and Congestion Window Reduced (CWR), to perform the handshakes for negotiating the usage of ECN between the endpoints during the setup of a TCP connection to determine if they are both ECN-capable. The ECE bit is further used by the data receiver to inform the data sender that a CE-marked packet has been receiver. The CWR bit is further used by the data sender to inform the data receiver that the congestion window has been reduced.